1. Field of the Invention
The present invention generally relates to tools for fabrication of electronic chips. Specifically, the technique provides for rapid quantification of critical profile characteristics for advanced semiconductor process monitoring and control.
2. Description of the Related Art
Conventional semiconductor wafer processing technology is rapidly developing structures such as lines, spaces, contacts, bars, vias, etc., with dimensions less than 130 nm. The edge, or profile, structural component at these dimensional tolerances becomes a significant percentage of the overall feature. At these dimensions, characteristics of the profile of an edge of any given feature may have severe impact on further processing or more importantly the final electrical response of devices and wiring.
FIG. 1 shows a typical conventional wafer with multiple chips fabricated thereon. As is well known in the art, a multitude of process steps during fabrication of semiconductor devices involve patterning of the various film stacks present on a substrate wafer. These patterns have many feature types including, but not limited to, lines, spaces, vias, contacts, studs, bars, and troughs. Although all of the features on a semiconductor wafer have a three dimensional structure, for larger feature geometries, only two-dimensional metrology is needed for process control.
Lithographic extension has resulted in production of sub-130 nm features. At these feature dimensions, the surface morphology, or surface characteristics, becomes a greater percentage of the bulk volume of the feature. Therefore, controlling these characteristics becomes critical for maintaining stable processes and reliable devices.
Control of semiconductor wafer processes has also evolved to include characteristics of profile as part of critical dimension specifications. That is, characteristics such as sidewall angle, corner rounding, edge roughness, and linearity are being used qualitatively to determine appropriate process window definitions. The current process typically involves taking a physical cross-section or using an atomic force microscope (AFM) equipment to obtain images after various process steps. Engineers use the images to determine the process space and the necessary process conditions to produce the desired effect. In-line quantitative process controls are limited by two-dimensional (top down) metrology which does not allow for full characterization of the process step. Therefore, only gross deviations from the process window are detected with respect to profile characteristics. Detailed analysis always requires engineering involvement with scrutiny over physical cross sections and three-dimensional imaging equipment data. This is an expensive and time-consuming task.
The most widely encountered features from a wafer processing stand point are the line, space, and contact hole (similar to a via). All three of these components contain edges (profiles). However, the orientation of the profile is different depending on the exact three dimensional structure being evaluated. A three dimensional representation of a line and space, as wells as profiles of edges across both features, is shown in FIG. 2 depicting the geometric differences of otherwise identical edges. A contact hole, not depicted, is simply a short axisymmetric space.
For simplicity, a left-handed profile (LH profile) is defined as a profile where the z-height increases as position moves from left to right. For a line feature, FIG. 2 (regions ABCD and EFGH), an example LH profile would be both the edges defined by regions AB and EF. More simply stated, a LH profile is the left hand side of the line as viewed in cross section. For an area such as a via, LH profile is the right hand side of the space.
In the semiconductor fabricator, meaning herein, for example, as either the process of fabricating semiconductor chips or the actual facility that does the fabrication process, three dimensional imaging (or inferencing) equipment such as the atomic force microscope (AFM), Scanning Electron Microscope (SEM), Scatterometer, and Transmission Electron Microscope (TEM) are used to qualitatively assess feature geometries beyond currently controlled parameters such as linewidth critical dimensions (CD) and film thicknesses. As previously mentioned, as features keep getting smaller, the edge component of a line is a greater percentage of the bulk structure. Characteristics such as sidewall angle (SWA), corner rounding, profile roughness (i.e. standing waves), etc., are common examples of what lithography and etch engineers are interested in controlling. However, engineering process window definitions are generally the only application for three dimensional imaging equipment due to the slower information acquisition times. Faster two dimensional imaging equipment is then used for process controls.
Recent breakthroughs in three dimensional metrology equipment are bringing forth tools that operate faster As a result, semiconductor process engineers will be able to obtain more three dimensional images for engineering analysis and process control. However, there currently are no quantitative metrology algorithms for determining critical feature characteristics. This invention provides a software analysis system that utilizes profile data to determine critical parameters that will extend process control capabilities into the future semiconductor device ground rules.